Experimental design
In Mid-August of 2021, field data were collected in two sites of the Tibetan semi-arid alpine steppe, Shrub encroachment has been prevalent in both the two sites, with one site encroached by a leguminous shrub (C. spinifera ) and the other site encroached by an none-leguminous shrub (D. fruticosa ). At each site, alpine steppe and shrub encroached alpine steppe were selected (Fig. 1a-d). At each of the AS and ASSE treatments, a 30 m × 30 m grassland plot was set, with the paired grassland plot and shrub encroached grassland plot separated by approximately 30 m. Within each plot, five 0.5 m × 0.5 m quadrats were sampled. Totally, 20 quadrats (2 shrub types × 10 quadrats) were sampled.